THE (ESOPHAGUS, STOMACHS AND INTESTINES. 415 



But even if uric acid has been found in the Malpighian tubes 

 of some insects, this does not prove their renal function, since 

 the liver contains a large quantity of urea in mammals and of 

 uric acid in birds. 



(5) ' The secretion of the Malpighian tubes agrees in no way 

 with the hepatic secretion.' 



Authors have repeatedly stated that the so-called bile tubes 

 of invertebrates never contain the bile acids, and Griffiths 

 [160] criticising my statements already published, says : ' It 

 may be stated in passing that according to B. T. Lowne the 

 Malpighian tubules of Calliphora Erythrocephala are " hepatic '' 

 in function. If by hepatic he means that these tubules have 

 the function of a vertebrate liver, his conclusions are erroneous, 

 for neither biliary acids nor glycogen are present in these 

 tubules. Again, if he means by " hepatic," they have a 

 pancreatic function ; this is also erroneous, because these 

 tubules do not yield any digestive ferment or ferments ' 

 (p. 96). 



These statements are sweeping, and would be serious if they 

 were accurate. I cannot positively state that the Malpighian 

 tubules of the Blow-fly or of its larva contain cholalic acid, but I 

 can positively affirm that those of the larva give Pettenkofer's 

 reaction with great brilliancy, which is, to say the least, an in- 

 dication, and a strong one, that they do contain cholalic acid 

 or some closely-allied substance. On moistening a portion 

 of the tubules with a weak solution of cane sugar, draining off 

 the excess and treating with dilute sulphuric acid, draining 

 off the excess again and heating carefully to dryness, they 

 become an intense cherry red, and the above is the most 

 delicate test I know for the presence of cholalic acid. 



I am quite aware that Pettenkofer's reaction is unfortunately 

 not distinctive of cholalic acid, and that it occurs in the 

 presence of proteids and other organic substances, thus the 

 fat bodies and even the blood of the larva give a brick-red 

 reaction with this test ; but, as Halliburton states,* no organic 



* 'Text-book of Chemical Physiology,' London and New York, 1891, 

 p. 682. 



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